The technology of heating and evaporating an organic material under vacuum environment to form a film of the organic material onto a substrate is known as evaporation coating technology (evaporation coating for short), which appeals those skilled in the art for its advantageous such as wider range of application and low pollution.
Generally, an evaporation coating process utilizes a line source, usually a heater strip, as the heating source, so as to improve film-forming efficiency and material utilization. One of known processes applying the evaporation coating technology based on line source into Organic Light-Emitting Diode (OLED) products comprises steps of adding an organic material into a crucible having a size matched with that of a substrate; heating the organic material in the crucible by a heater strip surrounding or attaching onto a periphery of the crucible so that the organic material subject to heating can be uniformly evaporated onto a surface of the substrate disposed at an upper side of the crucible through a plurality of evaporation holes formed at a top end of the crucible, so as to complete the film-forming process of the substrate in an OLED product.
At present, OLED products are developing towards larger size, which results in larger and larger sized substrate, and correspondingly larger and larger sized crucible and hence longer and longer line source for heating. It's therefore more difficult to control, for example, a uniform temperature of the line source for a large sized substrate, which leads to a worse uniformity of film-forming with the organic material on the surface of the substrate.